Described as a subspecies of P. darwini by Thomas (1912) and therewith ranked by others (Cabrera, 1961; Hershkovitz, 1962; Pearson, 1958). Steppan (1998) defended the specific status of limatus, including populations confused under P. xanthopygusrupestris, based on congruent morphological and molecular data; he further noted appreciable differentiation between northern and southern populations of P. limatus but declined to recognize these formally as subspecies. Sister species of P. xanthopygus according to maximum parsimony analyses of cytochrome b sequences (Steppan, 1998), perhaps arising by peripheral isolation from a western lineage of P. xanthopygusrupestris (Kuch et al., 2002). Late Quaternary occurrence of the species in the S Atacama Desert, slightly to the south of its current range, documented by mitochondrial DNA recovered from ancient rodent midden (Kuch et al., 2002).